This invention relates generally to a navigation system for use with an automobile, which system indicates the present location of the automobile on a displayed road map.
A prior art navigation system for use with an automobile is disclosed in Japanese Patent Provisional Publication (Kokai) No. 55-159299. This prior art system, comprises a distance sensor which measures the travelled distance of a motor vehile, and a direction sensor which detects the travelling diretion of the motor vehicle so that the present location of the motor vehicle is indicated on a road map associated with a display. This system, however, suffers from a drawback that it is troublesome to handle the same because various maps printed on transparent films have to be changed by taking one out of the display unit and inserting another one thereinto.
In order to remove the above-mentioned disadvantage, the inventors of the present invention have divised a system using a tape player which reads road map information from a cassette tape. Namely, a plurality of pieces of information each indicating a road map of a predetermined region or section are prerecorded in a cassette tape so that a desired piece of information can be selectively read out to image a corresponding road map on a display.
Stereophonic audio sound reproduction systems having a cassette tape player are widely used in motor vehicles nowadays. Therefore, if the cassette tape player or recorder used for such stereophonic sound reproduction system in motor vehicles can be used as the cassette tape player for deriving road map information, the navigation system will be manufactured with less cost, while it would be convenient to the users because manipulation of cassette tape players is very simple.
However, conventional cassette tape players, which are widely used for reproducing audio signals, cannot simply be adapted because it is necessary to detect whether the information derived from a cassette tape is either an audio signal, such as music, or data indicative of road map information. It is necessary to provide an arrangement for switching the output signal from the cassette player in accordance with the contents of a cassette tape loaded into the cassette player.